Field of the Invention
The present invention relates to wireless communications, and more specifically, to a method and apparatus for transmitting information in a wireless communication system.
Related Art
Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). A long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
Small cells using low power nodes are considered promising to cope with mobile traffic explosion, especially for hotspot deployments in indoor and outdoor scenarios. A low-power node generally means a node whose transmission (Tx) power is lower than macro node and base station (BS) classes, for example a pico and femto eNodeB (eNB) are both applicable. Small cell enhancements for 3GPP LTE will focus on additional functionalities for enhanced performance in hotspot areas for indoor and outdoor using low power nodes.
Some of activities will focus on achieving an even higher degree of interworking between the macro and low-power layers, including different forms of macro assistance to the low-power layer and dual-layer connectivity. Dual connectivity implies that the device has simultaneous connections to both macro and low-power layers. Macro assistance including dual connectivity may provide several benefits:                —Enhanced support for mobility—by maintaining the mobility anchor point in the macro layer, it is possible to maintain seamless mobility between macro and low-power layers, as well as between low-power nodes.        Low overhead transmissions from the low-power layer—by transmitting only information required for individual user experience, it is possible to avoid overhead coming from supporting idle-mode mobility within the local-area layer, for example.        Energy-efficient load balancing—by turning off the low-power nodes when there is no ongoing data transmission, it is possible to reduce the energy consumption of the low-power layer.        Per-link optimization—by being able to select the termination point for uplink and downlink separately, the node selection can be optimized for each link.        
Carrier aggregation (CA) may be introduced. In CA, two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. A Rel-10 UE with reception and/or transmission capabilities for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells. A Rel-8/9 UE can receive on a single CC and transmit on a single CC corresponding to one serving cell only.
When CA is configured, a user equipment (UE) only has one radio resource control (RRC) connection with the network. At RRC connection establishment/re-establishment/handover, one serving cell provides the non-access stratum (NAS) mobility information (e.g., tracking area identity (TAI)), and at RRC connection re-establishment/handover, one serving cell provides the security input. This cell is referred to as the primary cell (PCell). In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (DL PCC) while in the uplink it is the uplink primary component carrier (UL PCC).
Depending on UE capabilities, secondary cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a downlink secondary component carrier (DL SCC) while in the uplink it is an uplink secondary component carrier (UL SCC).
When the UE reports measurement results about one or more cells on one or more frequencies to the eNB, the eNB could send RRC connection reconfiguration to the UE in order to configure one or more SCells. Upon receiving the RRC connection reconfiguration including SCell configurations, the UE configures one or more SCells. Hence, the UE configures the SCell under the network's control.
A method for configuring the SCell more efficiently may be required.